Managing Herbicide Resistance: Should you Conserve or Exploit your Herbicides?

Herbicide resistance has become a major problem in dryland agriculture. In
Australia this particularly applies to annual ryegrass (Lolium rigidum) which
has developed multiple resistance to a wide range of commonly used
selective herbicides. Although herbicides are a very cost-effective means of
reducing weed density, major changes to their use are required if sustainable
weed management is to be achieved. In this study a model of ryegrass
population dynamics was used to identify the best integrated weed
management strategies and to evaluate changes in the economic payoff when
choosing to conserve herbicides rather than exploit them rapidly. A situation
of evolving herbicide resistance was simulated for a continuous wheat-lupin
rotation and two cropping sequences including one and two pasture phases.
Conservation of the last four shots of the selective herbicide Hoegrass was
found to be less profitable than their exploitation. Nevertheless, conservation
provided a better long-term weed control. Benefits from conservation were
lower in a situation of reduced level of weed control, but appeared to increase
with the inclusion of more pasture in the rotation.